Computation of Dielectric Properties from Short-Circuited Waveguide Measurements on High- or Low-Loss Materials (Computer Program Descriptions)

The complex permittivities (dielectric properties) of solid and pulverised samples of two plastics, Rexolite 1422 and Kynar, were measured at frequencies of 2.45, 11.5 and 22.0 GHz at 25 degrees C by the short-circuited waveguide technique. Several dielectric mixture equations and extrapolation of functions of the dielectric constants and loss factors that are linear with bulk density were then used to estimate the permittivities at solid-material densities from measurements on the pulverised samples. For these materials, the best estimates of the permittivities were provided by extrapolations that are consistent with the complex refractive index and Landau and Lifshitz, Looyenga mixture equations. The Bottcher mixture equation often gave values very close to the Landau and Lifshitz, Looyenga equation, and the Bruggeman-Hanai, Rayleigh and Lichtenecker mixture equations gave increasingly larger permittivity estimates in that order.

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Relationships between microwave permittivities of solid and pulverised plastics

Nelson

You

1990

J. Phys. D: Appl. Phys.

105

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A method for the evaluation of dielectric parameters of solids at microwave frequencies

Josyulu¹,

Krishna²,

Sobhanadri³

1982

J. Phys. E: Sci. Instrum.

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Dielectric properties of brain tissue between 0.01 and 10 GHz

Foster

Schepps

Stoy

et al. 1979

pmb

152

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Dielectric permittivity and conductivity are reported for grey and white matter from dog brain tissue between 0.01 and 10 GHz. Between 0.01 and approximately 1 GHz, the permittivity decreases and conductivity increases as a power law of frequency. Above 1 GHz, the conductivity increases quadratically with frequency due to dipolar reorientation of free water molecules in tissue; the apparent rotational relaxation frequency at 37 degrees C is 21--25 GHz, slightly below the 25 GHz characteristic frequency of pure water at that temperature. The microwave data are analysed using the Maxwell mixture theory applicable for a suspension of nonconducting, low permittivity spheres in bulk water. From the increase in conductivity above 1 GHz, and the tissue permittivity at 2--4 GHz, the apparent volume fraction of water is approximately 0.70 and 0.55 for grey and white matter, respectively, about 10--15% lower than respective values from the literature. This discrepancy is apparently due to a small fraction of water which does not contribute to the tissue permittivity above 1 GHz. Empirical equations are given to summarise the dielectric properties of 'average' brain tissue at 37 degrees C for future theoretical studies of microwave absorption in the head.

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Computation of Dielectric Properties from Short-Circuited Waveguide Measurements on High- or Low-Loss Materials (Computer Program Descriptions)

Cited by 7 publications

References 2 publications

Relationships between microwave permittivities of solid and pulverised plastics

Relationships between microwave permittivities of solid and pulverised plastics

A method for the evaluation of dielectric parameters of solids at microwave frequencies

Dielectric properties of brain tissue between 0.01 and 10 GHz

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